44 research outputs found
Star clusters in the triangulum galaxy: star cluster catalog and mass function fitting
No full texthonors thesisCollege of SciencePhysics & AstronomyAnil SethWe construct a catalog of star clusters in the Triangulum Galaxy (M33). The catalog is the result of the Local Group Cluster Search (LGCS) citizen science project through Zooniverse, where users classify images from the Hubble Space Telescope (HST). We base our star cluster catalog on the fraction of the 60 users that viewed each image who identified each object as a star cluster. We derive the completeness of the catalog from analyzing 1700 synthetic clusters to determine detection limits, as well as comparing our results to previous catalogs in the literature. By weighting Zooniverse users based on how many objects they classified as star clusters that were in fact star clusters, we improve catalog completeness. The catalog improves upon previous ground based catalogs extending the catalog by approximately 1300 clusters, providing base data for further research into star formation in M33. Using the star cluster catalog, we measure the cluster mass function for 290 young star clusters in M33 whose ages and masses were derived through integrated light spectral energy distribution fitting. Our mass function fitting uses a probabilistic Markov chain Monte Carlo technique. Although fits to integrated light observations lead to larger uncertainties than from other methods, a majority of extragalactic star cluster samples rely on integrated light fitting. We compare integrated light mass function fitting results in M31 to the mass function results for the exact same clusters whose ages and masses were derived through color magnitude diagram fitting previously published. We find the truncation mass log(Mc / M!) is 0.4 dex higher than the previously published CMD value, suggesting that uncertainties on the mass estimates of individual clusters can bias the upper mass truncation parameter of the cluster mass function to significantly higher values. We then run experiments using M51, M83 and NGC628 incorporating individual cluster mass errors into a simulated mass function fit. We find that the high errors of the integrated light method of deriving ages and masses systematically biases the truncation mass towards higher masses
Fine Tuning of Aperiodic Ordered Structures for Speech Intelligibility
No full textSpeech intelligibility is crucial in many spaces, yet designers often fail to predict the acoustic shortcomings of certain design choices. This paper builds on the potential of hybrid surface treatments showcasing low-frequency absorption to control background noise levels and high-frequency diffusion to improve speech-in-noise perception to introduce a workflow that encodes this information in a format easily perceived by designers. After patterns are being classified based on periodicity into partly periodic, non-periodic or aperiodic, a matrix serves as a rule of thumb communicating to non-experts the critical variables for high-frequency diffusion, such as well depth sequence, scale and profile. These become inputs of a computational process that generates variations to tailor patterns for speechintelligibility. Lastly, plotted graphs that visualize quantitative figures obtained from simulations are marked by a bounding box relative to the effective frequency range for designers to evaluate examined patterns during the process of optioneering. This integrated workflow targets architects and designers that seek for visual feedback to support an iterative exploration of performance driven geometries, while recognizing the contribution of aperiodic order to uniformly distribute the flow of sound energy.Design InformaticsBuilding Physic
Optimisation of Complex Geometry High-Rise Buildings based on Wind Load Analysis
No full textWind analysis for the structure of buildings is a challenging process. The increasing strength and frequency of wind events due to climate change only add higher demands. In addition, high-rise buildings are growing in number and include many of unconventional shape. Current methods used in practice for calculating structural wind response either do not account for these geometries, such as the Eurocode or are prohibitively time-consuming and expensive, such as physical wind tunnel tests and complex Computational Fluid Dynamics simulations. As such, wind loads are usually only considered towards the end of design. This paper presents the development of a computational method to analyse the effect of wind on the structural behaviour of a 3D building model and optimise the external geometry to reduce those effects at an early design phase. It combines Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA), and an Optimisation algorithm. This allows it to be used in an early design stage for performance-based design exploration in complement to the more traditional late-stage methods outlined above. The method was implemented into a rapid and easy to use computational tool by combining existing plugins in Grasshopper into a single script that can be used in practice on complex shaped parametric high-rise building models. After developing the method and testing the timeliness and precision of the CFD, and FEA portions on case study buildings, the tool was able to output an optimal geometry as well as a database of improved geometric options with their corresponding performance for the wind loading allowingfor performance-based decision-making in the early design phase.Design InformaticsStructural Design & Mechanic
A Performance-Driven Approach for the Design of Cellular Geometries with Low Thermal Conductivity for Application in 3D-Printed Façade Components
No full textAdditive manufacturing allows the fabrication of complex geometries with enhanced performances, making it interesting for application in façade components. Assessing the performance of non-standard geometries and 3D printed parts requires a combination of digital and analytical methods to retrieve validated models which can guide the design process. In this study a 3D printed mono-material façade component was designed, where the complex geometrical configuration enhance its thermal insulation properties. For this, a digital workflow was developed, encompassing performance-driven design, performance assessment and geometry generation for fabrication.Analytical heat transfer models, heat flux measurements, and heat transfer simulations with COMSOL Multiphysics were used to assess the thermal properties of different geometrical alternatives. By observing and comparing the results, a validated model was defined to retrieve design guidelines and thermal performance indicators. The results identify porosity as the driving factor for thermal insulation and clarify the nature of the heat transfer in 3D printed cellular structures. Open surface-based geometries were preferred for the good combination of thermal properties and manufacturability. The findings are embedded in a digital workflow in Rhino-Grasshopper, enabling the design of insulating cellular structures to be used in 3D printed façade components.Design InformaticsBuilding Physic
Retinal Image Quality Analysis For Automatic Diabetic Retinopathy Detection
No full textSufficient image quality is a necessary prerequisite for reliable automatic detection systems in several healthcare environments. Specifically for Diabetic Retinopathy (DR) detection, poor quality fund us makes more difficult the analysis of discontinuities that characterize lesions, as well as to generate evidence that can incorrectly diagnose the presence of anomalies. Several methods have been applied for classification of image quality and recently, have shown satisfactory results. However, most of the authors have focused only on the visibility of blood vessels through detection of blurring. Furthermore, these studies frequently only used fund us images from specific cameras which are not validated on datasets obtained from different retinographers. In this paper, we propose an approach to verify essential requirements of retinal image quality for DR screening: field definition and blur detection. The methods were developed and validated on two large, representative datasets collected by different cameras. The first dataset comprises 5,776 images and the second, 920 images. For field definition, the method yields a performance close to optimal with an area under the Receiver Operating Characteristic curve (ROC) of 96.0%. For blur detection, the method achieves an area under the ROC curve of 95.5%. © 2012 IEEE.229236Saaddine, J., Honeycutt, A., Narayan, K., Zhang, X., Klein, R., Boyle, J., Projection of diabetic retinopathy and other major eye diseases among people with diabetes mellitus: United states, 2005-2050 (2008) Arch Ophthalmol., 126 (12), pp. 1740-1747Spurling, G., Askew, D., Hansar, N.H.N., Cooney, A., Jackson, C., Retinal photography for diabetic retinopathy screening in indigenous primary health care: The inala experience (2010) Australian and New Zealand Journal of Public Health, 34, pp. S30-S33Pettitt, D.J., Wollitzer, A.O., Jovanovic, L., He, G., Ipp, E., Decreasing the risk of diabetic retinopathy in a study of case management: The California medi-cal type 2 diabetes study (2005) Diabetes Care, 28 (12), pp. 2819-2822. , http://care.diabetesjournals.org/cgi/reprint/28/12/2819, DOI 10.2337/diacare.28.12.2819Bragge, P., Gruen, R., Chau, M., Forbes, A., Taylor, H., Screening for presence or absence of diabetic retinopathy: A meta-analysis (2011) Arch Ophthalmol., 129 (4), pp. 435-444Maberley, D., Morris, A., Hay, D., Chang, A., Hall, L., Mandava, N., A comparison of digital retinal image quality among photographers with different levels of training using a non-mydriatic fundus camera (2004) Ophthalmic Epidemiology, 11 (3), pp. 191-197. , DOI 10.1080/09286580490514496Philip, S., Fleming, A.D., Goatman, K.A., Fonseca, S., Mcnamee, P., Scotland, G.S., Prescott, G.J., Olson, J.A., The efficacy of automated "disease/no disease" grading for diabetic retinopathy in a systematic screening programme (2007) British Journal of Ophthalmology, 91 (11), pp. 1512-1517. , DOI 10.1136/bjo.2007.119453Jelinek, H., Cree, M., (2010) Automated Image Detection of Retinal Pathology, , Boca Raton: CRC PressDavis, H., Russell, S., Barriga, E., Abramoff, M., Soliz, P., Visionbased, real-time retinal image quality assessment (2009) IEEE CMBS, pp. 1-6Giancardo, L., Meriaudeau, F., Karnowski, T., Chaum, E., Tobin, K., (2010) New Developments in Biomedical Engineering, pp. 201-224. , InTech, ch. Quality Assessment of Retinal Fundus Images using Elliptical Local Vessel DensityLalonde, M., Gagnon, L., Boucher, M.-C., Automatic visual quality assessment in optical fundus images (2001) Vision Interface, pp. 259-264Niemeijer, M., Abramoff, M.D., Van Ginneken, B., Image structure clustering for image quality verification of color retina images in diabetic retinopathy screening (2006) Medical Image Analysis, 10 (6), pp. 888-898. , DOI 10.1016/j.media.2006.09.006, PII S1361841506000739Patton, N., Aslam, T.M., MacGillivray, T., Deary, I.J., Dhillon, B., Eikelboom, R.H., Yogesan, K., Constable, I.J., Retinal image analysis: Concepts, applications and potential (2006) Progress in Retinal and Eye Research, 25 (1), pp. 99-127. , DOI 10.1016/j.preteyeres.2005.07.001, PII S1350946205000406Jelinek, H., Rocha, A., Carvalho, T., Goldenstein, S., Wainer, J., Machine learning and pattern classification in identification of indigenous retinal pathology (2011) IEEE EMBSFacey, K., (2002) Health Tech. Assessment: Organisation of Services for Diabetic Retinopathy Screening, , Health Tech. Board for ScotlandFleming, A.D., Philip, S., Goatman, K.A., Olson, J.A., Sharp, P.F., Automated assessment of diabetic retinal image quality based on clarity and field definition (2006) Investigative Ophthalmology and Visual Science, 47 (3), pp. 1120-1125. , DOI 10.1167/iovs.05-1155Winn, J., Criminisi, A., Minka, T., Object categorization by learned universal visual dictionary (2005) Proceedings of the IEEE International Conference on Computer Vision, 2, pp. 1800-1807. , DOI 10.1109/ICCV.2005.171, 1544935, Proceedings - 10th IEEE International Conference on Computer Vision, ICCV 2005Herbert, J., Pires, R., Padilha, R., Goldenstein, S., Wainer, J., Bossomaier, T., Rocha, A., Data fusion for multi-lesion diabetic retinopathy detection IEEE EMBS, 2012Wang, Z., Bovik, A., Sheikh, H., Simoncelli, E., Image quality assessment: From error visibility to structural similarity (2004) IEEE Trans. on Image Processing, 13 (4), pp. 600-612Pizer Stephen, M., Amburn, E.P., Austin John, D., Cromartie, R., Geselowitz, A., Greer, T., Ter Haar Romeny, B., Zuiderveld, K., Adaptive histogram equalization and its variations (1987) Computer vision, graphics, and image processing, 39 (3), pp. 355-368Chang, C.-C., Lin, C.-J., LIBSVM: A library for support vector machines (2011) ACM Trans. on Intelligent Systems and Tech., 2, pp. 2701-2727Gonzalez, R., Woods, R., (2006) Digital Image Processing, , (3rd Ed.). Upper Saddle River, NJ, USA: Prentice-Hall, IncBay, H., Tuytelaars, T., Van Gool, L., SURF: Speeded up robust features (2006) Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 3951, pp. 404-417. , DOI 10.1007/11744023-32, Computer Vision - ECCV 2006, 9th European Conference on Computer Vision, ProceedingsSivic, J., Zisserman, A., Video google: A text retrieval approach to object matching in videos (2003) IEEE ICCV, pp. 1470-1477Do Valle Jr., E.A., (2008) Local-descriptor Matching for Image Identification Systems, , Ph.D. dissertation, Université de Cergy-Pontoise École Doctorale Sciences et Ingénierie, Cergy-Pontoise, France, JuneRocha, A., Papa, J., Meira, L., How far do we get using machine learning black-boxes? Intl. Journal of Pattern Recognition and Artificial Intelligence, 2012, pp. 1-
Advancing Bag-of-Visual-Words Representations for Lesion Classification in Retinal Images
No full textDiabetic Retinopathy (DR) is a complication of diabetes that can lead to blindness if not readily discovered. Automated screening algorithms have the potential to improve identification of patients who need further medical attention. However, the identification of lesions must be accurate to be useful for clinical application. The bag-of-visual-words (BoVW) algorithm employs a maximum-margin classifier in a flexible framework that is able to detect the most common DR-related lesions such as microaneurysms, cotton-wool spots and hard exudates. BoVW allows to bypass the need for pre- and post-processing of the retinographic images, as well as the need of specific ad hoc techniques for identification of each type of lesion. An extensive evaluation of the BoVW model, using three large retinograph datasets (DR1, DR2 and Messidor) with different resolution and collected by different healthcare personnel, was performed. The results demonstrate that the BoVW classification approach can identify different lesions within an image without having to utilize different algorithms for each lesion reducing processing time and providing a more flexible diagnostic system. Our BoVW scheme is based on sparse low-level feature detection with a Speeded-Up Robust Features (SURF) local descriptor, and mid-level features based on semisoft coding with max pooling. The best BoVW representation for retinal image classification was an area under the receiver operating characteristic curve (AUC-ROC) of 97.8% (exudates) and 93.5% (red lesions), applying a cross-dataset validation protocol. To assess the accuracy for detecting cases that require referral within one year, the sparse extraction technique associated with semi-soft coding and max pooling obtained an AUC of 94.2±2.0%, outperforming current methods. Those results indicate that, for retinal image classification tasks in clinical practice, BoVW is equal and, in some instances, surpasses results obtained using dense detection (widely believed to be the best choice in many vision problems) for the low-level descriptors. © 2014 Pires et al.96Sinthanayothin, C., Boyce, J.F., Williamson, T.H., Cook, H.L., Mensah, E., Lal, S., Usher, D., Automated detection of diabetic retinopathy on digital fundus images (2002) Diabetic Medicine, 19 (2), pp. 105-112. , DOI 10.1046/j.1464-5491.2002.00613.xJelinek, H.F., Cree, M.J., Worsley, D., Luckie, A.P., Nixon, P., An automated microaneurysm detector as a tool for identification of diabetic retinopathy in rural optometric practice (2006) Clinical and Experimental Optometry, 89, pp. 299-305Fleming, A.D., Philip, S., Goatman, K.A., Olson, J.A., Sharp, P.F., Automated microaneurysm detection using local contrast normalization and local vessel detection (2006) IEEE Transactions on Medical Imaging, 25 (9), pp. 1223-1232. , DOI 10.1109/TMI.2006.879953, 1677728Niemeijer, M., Van Ginneken, B., Russell, S.R., Suttorp-Schulten, M.S.A., Abramoff, M.D., Automated detection and differentiation of drusen, exudates, and cotton-wool spots in digital color fundus photographs for diabetic retinopathy diagnosis (2007) Investigative Ophthalmology and Visual Science, 48 (5), pp. 2260-2267. , DOI 10.1167/iovs.06-0996Giancardo, L., Mériaudeau, F., Karnowski, T.P., Tobin, K.W., Li, Y., Microaneurysms Detection with the Radon Cliff Operator in Retinal Fundus Images (2010) SPIE Medical Imaging, pp. 76230U-76230U. , International Society for Optics and PhotonicsAntal, B., Hajdu, A., An Ensemble-based System for Microaneurysm Detection and Diabetic Retinopathy Grading (2012) IEEE Transactions on Biomedical Engineering, 59 (6), pp. 1720-1726Lazar, I., Hajdu, A., Retinal Microaneurysm Detection Through Local Rotating Cross-section Profile Analysis (2013) IEEE Transactions on Medical Imaging, 32 (2), pp. 400-407Zhang, B., Wu, X., You, J., Li, Q., Karray, F., Hierarchical Detection of Red Lesions in Retinal Images by Multiscale Correlation Filtering (2009) SPIE Medical Imaging, pp. 72601L-72601L. , International Society for Optics and PhotonicsSánchez, C.I., Hornero, R., Mayo, A., García, M., Mixture model-based clustering and logistic regression for automatic detection of microaneurysms in retinal images (2009) SPIE Medical Imaging, pp. 72601M-72601M. , International Society for Optics and PhotonicsSánchez, C.I., García, M., Mayo, A., López, M.I., Hornero, R., Retinal image analysis based on mixture models to detect hard exudates (2009) Medical Image Analysis, 13 (4), pp. 650-658Giancardo, L., Meriaudeau, F., Karnowski, T.P., Li, Y., Garg, S., Tobin, K.W., Chaum, E., Exudate-based diabetic macular edema detection in fundus images using publicly available datasets (2012) Medical Image Analysis, 16 (1), pp. 216-226Fleming, A.D., Philip, S., Goatman, K.A., Williams, G.J., Olson, J.A., Sharp, P.F., Automated detection of exudates for diabetic retinopathy screening (2007) Physics in Medicine and Biology, 52 (24), pp. 7385-7396. , DOI 10.1088/0031-9155/52/24/012, PII S0031915507570430Sopharak, A., Uyyanonvara, B., Barman, S., Williamson, T.H., Automatic detection of diabetic retinopathy exudates from non-dilated retinal images using mathematical morphology methods (2008) Computerized Medical Imaging and Graphics, 32, p. 8Welfer, D., Scharcanski, J., Marinho, D.R., A coarse-to-fine strategy for automatically detecting exudates in color eye fundus images (2010) Computerized Medical Imaging and Graphics, 34, pp. 228-235Boureau, Y., Bach, F., LeCun, Y., Ponce, J., Learning mid-level features for recognition (2010) IEEE Intl. Conference on Computer Vision and Pattern RecognitionRocha, A., Carvalho, T., Jelinek, H.F., Goldenstein, S., Wainer, J., Points of interest and visual dictionaries for automatic retinal lesion detection (2012) IEEE Transactions on Biomedical Engineering, 59, pp. 2244-2253Jelinek, H.F., Rocha, A., Carvalho, T., Goldenstein, S., Wainer, J., Machine learning and pattern classification in identification of indigenous retinal pathology (2011) Intl. Conference of the IEEE Engineering in Medicine and Biology Society, pp. 5951-5954Jelinek, H.F., Pires, R., Padilha, R., Goldenstein, S., Wainer, J., Data fusion for multi-lesion diabetic retinopathy detection (2012) IEEE Intl. Computer-Based Medical Systems, pp. 1-4Phillips, P.J., Visible manifestations of diabetic retinopathy (2012) Medicine Today, 5, p. 83(2013) Diabetes Programme. Online, , http://www.who.int/diabetes/en, World Health Organization Available: Accessed 6 May 2014Giancardo, L., Meriaudeau, F., Karnowski, T.P., Li, Y., Tobin, K., Microaneurysm detection with radon transform-based classification on retina images (2011) Intl. Conference of the IEEE Engineering in Medicine and Biology Society, pp. 5939-5942Li, Y., Karnowski, T.P., Tobin, K.W., Giancardo, L., Morris, S., A health insurance portability and accountability act-compliant ocular telehealth network for the remote diagnosis and management of diabetic retinopathy (2011) Telemedicine and E-Health, 17, pp. 627-634Cree, M.J., Gamble, E., Cornforth, D.J., Colour normalisation to reduce interpatient and intrapatient variability in microaneurysm detection in colour retinal images (2005) Workshop on Digital Image Computing, pp. 163-168Soares, J.V.B., Leandro, J.J.G., Cesar Jr., R.M., Jelinek, H.F., Cree, M.J., Retinal vessel segmentation using the 2-D Gabor wavelet and supervised classification (2006) IEEE Transactions on Medical Imaging, 25 (9), pp. 1214-1222. , DOI 10.1109/TMI.2006.879967, 1677727Acharya, U.R., Lim, C.M., Ng, E.Y.K., Chee, C., Tamura, T., Computer-based detection of diabetes retinopathy stages using digital fundus images (2009) Journal of Engineering in Medicine, 223, pp. 545-553Gonzalez, R.C., Woods, R.E., (2006) Digital Image Processing, , Upper Saddle River, NJ, USA: PrenticeHall, Inc., 2nd editionNayak, J., Bhat, P.S., Acharya, U.R., Lim, C.M., Kagathi, M., Automated identification of diabetic retinopathy stages using digital fundus images (2008) Journal of Medical Systems, 32, pp. 107-115Jelinek, H.F., Al-Saedi, K., Backlund, L.B., Computer assisted 'top-down' assessment of diabetic retinopathy (2009) World Congress on Medical Physics and Biomedical Engineering, pp. 127-130Yun, W.L., Rajendra, A.U., Venkatesh, Y.V., Chee, C., Min, L.C., Ng, E.Y.K., Identification of different stages of diabetic retinopathy using retinal optical images (2008) Information Sciences, 178 (1), pp. 106-121. , DOI 10.1016/j.ins.2007.07.020, PII S0020025507003635Sivic, J., Zisserman, A., Video Google: A Text Retrieval Approach to Object Matching in Videos (2003) IEEE Intl. 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ETDRS Report Number 10 (1991) Ophthalmology, 98, pp. 786-806. , ETDRS Research GroupMitchell, P., Foran, S., Wong, T.Y., Chua, B., Patel, I., (2008) Guidelines for the Management of Diabetic Retinopathy, , http://www.nhmrc.gov.au/_files_nhmrc/file/publications/synopses/di15.pdf, Available: Accessed: 6 May 2014Chew, E.Y., A simplified diabetic retinopathy scale (2003) Ophthalmology, 110 (9), pp. 1675-1676. , SepAbramoff, M.D., Niemeijer, M., Suttorp-Schulten, M.S.A., Viergever, M.A., Russell, S.R., Van Ginneken, B., Evaluation of a system for automatic detection of diabetic retinopathy from color fundus photographs in a large population of patients with diabetes (2008) Diabetes Care, 31 (2), pp. 193-198. , http://care.diabetesjournals.org/cgi/reprint/31/2/193, DOI 10.2337/dc07-1312Fleming, A.D., Goatman, K.A., Philip, S., Williams, G.J., Prescott, G.J., The role of haemorrhage and exudate detection in automated grading of diabetic retinopathy (2010) British Journal of Ophthalmology, 94 (6), pp. 706-711Abramoff, M.D., Folk, J.C., Han, D.P., Walker, J.D., Williams, D.F., Automated analysis of retinal images for detection of referable diabetic retinopathy (2013) JAMA Ophthalmol, 131 (3), pp. 351-357Ahmed, J., Ward, T.P., Bursell, S.-E., Aiello, L.M., Cavallerano, J.D., Vigersky, R.A., The sensitivity and specificity of nonmydriatic digital stereoscopic retinal imaging in detecting diabetic retinopathy (2006) Diabetes Care, 29 (10), pp. 2205-2209. , http://care.diabetesjournals.org/cgi/reprint/29/10/2205.pdf, DOI 10.2337/dc06-0295Chatfield, K., Lempitsky, V., Vedaldi, A., Zisserman, A., The devil is in the details: An evaluation of recent feature encoding methods (2011) British Machine Vision Conference (BMVC), pp. 1-12Perronnin, F., Akata, Z., Harchaoui, Z., Schmid, C., Towards good practice in large-scale learning for image classification (2012) Intl. 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Evolution in the number of authors of computer science publications
No full textThis article analyses the evolution in the number of authors of scientific publications in computer science (CS). This analysis is based on a framework that structures CS into 17 constituent areas, proposed by Wainer et al. (Commun ACM 56(8):67–63, 2013), so that indicators can be calculated for each one in order to make comparisons. We collected and mined over 200,000 article references from 81 conferences and journals in
the considered CS areas, spanning a 60-year period (1954–2014). The main insights of this article are that all CS areas witness an increase in the average number of authors, in every decade, with just one slight exception. We ordered the article references by number of authors, in ascending chronological order and grouped them into decades. For each CS area, we provide a perspective of how many groups (1-author papers, 2-author papers and so on) must be considered to reach certain proportions of the total for that CS area, e.g., the 90th and 95th percentiles. Different CS areas require different number of groups to reach those percentiles. For all 17 CS areas, an analysis of the point in time in which publications with n+1 authors overtake the publications with n authors is presented. Finally, we analyse the average number of authors and their rate of increase.This work was supported by FCT - Fundação para a Ciência e Tecnologia within the Project Scope UID/CEC/00319/2013
Transmucosal nasal drug delivery : pharmacokinetics and pharmacodynamics of nasally applied esketamine
No full textPrice-based capital account regulations: the Colombian experience
No full textThe Chilean experience with price-based capital account regulations (i.e., deposits or reserve requirements on capital inflows) has been subject to extensive discussion in the recent literature. This paper presents evidence on the effectiveness of similar regulations in Colombia since September 1993, when traditional exchange controls were replaced by price-based regulations. It is important to emphasize that the Tobin tax equivalent of such regulations in Colombia has been quite high (13.6% and 6.4% tax for 12 and 36 months loans, respectively, in 1994-1998), and, as in Chile, it is certainly much higher than the rates suggested for an international Tobin tax. The econometric evidence presented indicates that these regulations have been effective in Colombia, both in terms of reducing the volume of flows and in improving the term structure of external borrowing. This indicates that price-based regulations give the authorities some room for maneuver to adopt restrictive monetary policies during international capital market booms. They have also been effective in improving the debt profile of the country, a crucial determinant of macroeconomic risks in the face of busts in the international capital market.
Searching for Stellar Activity Cycles Using Flares: The Short- and Long-timescale Activity Variations of TIC-272272592
No full textWe examine 4 yr of Kepler 30 minutes data, and five sectors of Transiting Exoplanet Survey Satellite 2 minutes data for the dM3 star KIC-8507979/TIC-272272592. This rapidly rotating ( P = 1.2 day) star has previously been identified as flare active, with a possible long-term decline in its flare output. Such slow changes in surface magnetic activity are potential indicators of solar-like activity cycles, which can yield important information about the structure of the stellar dynamo. We find that while TIC-272272592 shows evidence for both short- and long-timescale variations in its flare activity, it is unlikely physically motivated. Only a handful of stars have been subjected to such long-baseline point-in-time flare studies, and we urge caution in comparing results between telescopes due to differences in bandpass, signal-to-noise ratio, and cadence. In this work, we develop an approach to measure variations in the flare frequency distributions over time, which is quantified as a function of the observing baseline. For TIC-272272592, we find a 2.7 σ detection of a sector which has a flare deficit, therefore indicating the short-term variation could be a result of sampling statistics. This quantifiable approach to describing flare-rate variation is a powerful new method for measuring the months-to-years changes in surface magnetic activity, and provides important constraints on activity cycles and dynamo models for low-mass stars
